Method and Apparatus for Determining Existence of Foreign Material on Surface of Fingerprint Sensor, and Terminal

ABSTRACT

A method and an apparatus for determining existence of a foreign material on a surface of a fingerprint sensor, and a terminal are provided. The method includes the following. A current capacitance value of the fingerprint sensor of the terminal is obtained. A first difference between the current capacitance value and a preset capacitance reference value is calculated. Determine that the foreign material is present on the surface of the fingerprint sensor when the first difference is within a preset foreign-material threshold range.

CROSS-REFERENCE TO RELATED APPLICATION(S)

This application is a continuation of International Application No.PCT/CN2016/091802, filed on Jul. 26, 2016, which claims priority toChinese Patent Application No. 201510681166.9, filed on Oct. 19, 2015,the contents of both of which are hereby incorporated by reference intheir entireties.

TECHNICAL FIELD

The present disclosure relates to the field of terminal technology, andparticularly to a method and an apparatus for determining existence of aforeign material on a surface of a fingerprint sensor, and a terminal.

BACKGROUND

As terminal technologies and image processing technologies advance,fingerprint recognition technology, as a high-security recognitiontechnology, has been applied to many fields. The fingerprint recognitiontechnology can bring security protection for individual private devicesand is convenient for users. For example, terminals, applicationsoftware or files of the terminal can be encrypted or decrypted (inother words, locked or unlocked) via the fingerprint recognitiontechnology, to provide a better experience for the users.

The fingerprint recognition technology needs the user to touch a surfaceof a fingerprint sensor of the terminal with a finger, to acquirefingerprint information of the user. Inevitably, in a process ofacquiring the fingerprint information of the user, water or otherforeign materials (also known as a foreign object) may be present on thesurface of the fingerprint sensor or the finger of the user. Methods fordetermining existence of a foreign material on a surface of afingerprint sensor tend to be complicated without high accuracy.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a flowchart illustrating a method for determining existence ofa foreign material on a surface of a fingerprint sensor according to afirst implementation of the present disclosure.

FIG. 2 is a flowchart illustrating a method for determining existence ofa foreign material on a surface of a fingerprint sensor according to asecond implementation of the present disclosure.

FIG. 3 is a schematic structural diagram illustrating an apparatus fordetermining existence of a foreign material on a surface of afingerprint sensor according to a third implementation of the presentdisclosure.

FIG. 4 is a schematic structural diagram illustrating a terminalaccording to a fourth implementation of the present disclosure.

DETAILED DESCRIPTION

To describe the objectives, technical solutions, and advantages ofimplementations of the present disclosure more clearly, theimplementations of the present disclosure are further described indetail below with reference to the accompanying drawings. It should benoted that the implementations described herein are merely used toexplain rather than to limit the present disclosure. In addition, tofacilitate description, a part of contents related to the presentdisclosure rather than all the contents are illustrated in theaccompanying drawings. Prior to interpreting the exemplaryimplementations in detail, it should be mentioned that some exemplaryimplementations are described as processes or methods depicted as aflowchart. Although various operations (or steps) in the flowchart aredescribed as sequential processes, these operations can be performed inparallel, concurrently, or synchronously. Moreover, orders of theseoperations can be rearranged. The process may be terminated when theoperation thereof is completed, and additional steps may not be includedin the accompanying drawings. The processes may correspond to methods,functions, procedures, subroutines, subroutines, and the like.

In the following, some of the terms used herein are explained tofacilitate the understanding for those skilled in the art.

Terminal

Terminal, also known as a terminal device, terminal equipment, or userequipment (UE), means an electronic device that provides voice and/ordata connectivity to a user, examples of which can be hand-held deviceswith wireless connectivity function, on-board devices, or the like.Common terminals can be, for example, mobile phones, tablets, laptops,handheld computers, mobile internet devices (MID), or wearable equipmentsuch as smart watches, smart bracelets, and pedometers or others.Terminals in the present disclosure are not limited to mobile terminalsand common terminals, but can also be automated teller machines (ATM),ticket machines, entrance guard machines, medical equipment, or otherterminals equipped with fingerprint recognition function.

Fingerprint Sensor

A fingerprint sensor, also known as a fingerprint recognition module orfingerprint recognition sensor, can realize the recognition ofindividual fingerprint features through a specific induction sensor. Atpresent, the fingerprint recognition sensor is mainly divided into anoptical fingerprint sensor, a capacitive fingerprint sensor, and a radiofrequency (RF) fingerprint sensor. The fingerprint recognition sensorcan be set in combination with a metal dome array (in other words, domekey) of a terminal, and can be set on the front surface, the racesurface, or the side surface of the terminal, the present disclosure isnot limited thereto. Similarly, the fingerprint recognition sensor canbe set in combination with the touch screen of the terminal. Forexample, the fingerprint recognition sensor can be set below the touchpanel of the touchscreen.

In WO2011/108582 JA entitled “FOREIGN OBJECT DETERMINATION DEVICE,FOREIGN OBJECT DETERMINATION METHOD, AND FOREIGN OBJECT DETERMINATIONPROGRAM”, a foreign object determination scheme based on an image isprovided. The present disclosure provides a new technical solution todetermine foreign materials present on a surface of a fingerprint sensorbased on capacitance values of the fingerprint sensor. In the methodprovided herein, a current capacitance value is obtained and comparedwith a reference capacitance value (hereinafter, referred to as presetcapacitance reference value), and the terminal may determine whether ornot there is a foreign material on the surface of the fingerprint sensorbased on the comparison between the current capacitance value and thereference capacitance value.

First Implementation

FIG. 1 is a flowchart illustrating a method for determining existence ofa foreign material on a surface of a fingerprint sensor according to afirst implementation of the present disclosure. The method can beexecuted by an apparatus for determining the existence of a foreignmaterial on a surface of a fingerprint sensor. The apparatus can beimplemented by software and/or hardware and can be embedded in aterminal as a part of the terminal. As illustrated in FIG. 1, the methodof the implementation includes the following.

At block 101, a current capacitance value of the fingerprint sensor of aterminal is obtained.

The “terminal” referred to herein includes but is not limited to devicesequipped with a fingerprint sensor, such as mobile phones, tabletcomputers, laptops, or the like.

In the implementation, a current state of the fingerprint sensor of theterminal can be a state of the fingerprint sensor before or after a useracts on (for example, touches or presses) the fingerprint sensor.

At block 102, a first difference between the current capacitance valueand a preset capacitance reference value is calculated.

The preset capacitance reference value is obtained with no foreignmaterial present on the surface of the fingerprint sensor before leavingthe factory, and is stored in a system (such as a memory of theterminal) in advance.

At block 103, determine that the foreign material is present on or existon the surface of the fingerprint sensor when the first difference iswithin a preset foreign-material threshold range.

When the foreign material is present on the surface of the fingerprintsensor, the foreign material may be on the surface of the fingerprintsensor, or left on the surface of the fingerprint sensor after the usertouches the fingerprint sensor with the finger with the foreign materialthereon.

In the implementation, the foreign material is conductive and therefore,whether the foreign material is present on the surface of thefingerprint sensor can be determined according to capacitance valuechanges of the fingerprint sensor. The foreign material includes but isnot limited to water.

The preset foreign-material threshold range is set in advance accordingto experimental data of capacitance-change tests performed on thefingerprint sensor when different conductive foreign materials arepresent on the surface of the fingerprint sensor. The presetforeign-material threshold range can be determined according todifferent foreign materials on the surface of the fingerprint sensor inactual use.

In the case where the user touches the surface of the fingerprint sensorwith a finger when no foreign material is present on the surface of thefingerprint sensor, the capacitance value change of the fingerprintsensor relative to the preset capacitance reference value will be large;on the contrary, the capacitance value change of the fingerprint sensorrelative to the preset capacitance reference value will be small whenthe foreign material is present on the surface of the fingerprintsensor. When the difference between the current capacitance value of thefingerprint sensor and the preset capacitance reference value is withinthe preset foreign-material threshold range, determine that the foreignmaterial is on the surface of the fingerprint sensor.

According to the method for determining the existence of the foreignmaterial on the surface of the fingerprint sensor of the firstimplementation, by detecting the difference between the currentcapacitance value of the fingerprint sensor and the preset capacitancereference value, whether the difference is within the presetforeign-material threshold range is determined. Then determine theforeign material is present on the surface of the fingerprint sensor,when the difference is within the preset foreign-material thresholdrange. In other words, whether the foreign material is present on thesurface of the fingerprint sensor is determined according to thecapacitance value change of the fingerprint sensor, thereby simplifyingthe operation of determining existence of the foreign material presenton the surface of the fingerprint sensor of the terminal and improvingthe accuracy of determining existence of the foreign material present onthe surface of the fingerprint sensor of the terminal.

Second Implementation

FIG. 2 is a flowchart illustrating a method for determining existence ofa foreign material on a surface of a fingerprint sensor according to asecond implementation of the present disclosure. The implementation isfurther optimized on the basis of the first implementation. In theimplementation, the method may further include removing the foreignmaterial in a preset manner after determining that the foreign materialis present on the surface of the fingerprint sensor.

As illustrated in FIG. 2, the method of the implementation includes thefollowing.

At block 201, a current capacitance value of the fingerprint sensor of aterminal is obtained. In actual practice, the current capacitance valuecan be obtained at preset intervals such as one hour, ten minutes,thirty seconds, and the like. The current capacitance value can even beobtained continuously, which may, however, cause power consumptionproblem. Alternatively, the obtaining of the current capacitance valuecan be triggered by a certain event, such as a press or touch operationon the fingerprint sensor by a user.

The term “current capacitance value” indicates a capacitance value ofthe fingerprint sensor in the current state, and is dynamically changedrather than fixed as time goes on. The “current capacitance value”mentioned at block 201 can be understood as “first current capacitancevalue” to be distinguished from the “current capacitance value”mentioned at block 204-3.

At block 202, a first difference between the current capacitance valueand a preset capacitance reference value is calculated.

At block 203, if the first difference is within a presetforeign-material threshold range, determine that the foreign material ispresent on the surface of the fingerprint sensor. Otherwise, determinethe surface of the fingerprint sensor with no foreign material.

At block 204, the foreign material is removed in a preset manner.

In one implementation, the foreign material can be removed by increasingtemperature; in another implementation, the foreign material can beremoved by informing the user to remove it, such as issue an alert. Thepresent disclosure is not limited thereto.

Manner 1

As illustrated in FIG.2 at block 204-1, the terminal may send a messageor information indicating that the foreign material is present on thesurface of the fingerprint sensor, so as to prompt a user to remove theforeign material.

The message sent to the user can be a text prompt message, a soundprompt message, or a combination of both, and the implementation is notlimited thereto.

Manner 2

As illustrated in FIG.2 at block 204-2, the foreign material can beremoved by increasing a temperature of the fingerprint sensor.

The temperature of the fingerprint sensor can be improved in variousways. For example, the temperature of the fingerprint sensor can beincreased by increasing a power of the fingerprint sensor. Or, thetemperature of the fingerprint sensor can be increased by controlling aheating device corresponding to the fingerprint sensor to heat thefingerprint sensor.

The power of the fingerprint sensor can be increased at a constant rateor a step-changed rate. Likewise, the fingerprint sensor can be heatedat a constant rate or a step-changed rate by controlling the heatingdevice corresponding to the fingerprint sensor. The implementation ofthe disclosure is not limited thereto.

When a preset time has elapsed after increasing the temperature of thefingerprint sensor, the current capacitance value (can be referred to as“second current capacitance value” to be distinguished from the “currentcapacitance value” mentioned at block 201) of the fingerprint sensor ofthe terminal is obtained at block 204-3. A second difference between thecurrent capacitance value and the preset capacitance reference value isthen calculated at block 204-4. Then determine that the foreign materialis present on the surface of the fingerprint sensor at block 204-5 whenthe second difference is within the preset foreign-material thresholdrange. Thereafter, the method proceeds to block 204-1, to send themessage indicating that the foreign material is present on the surfaceof the fingerprint sensor, so as to prompt the user to remove theforeign material.

The preset time can be set in advance according to the performance ofheating the fingerprint sensor by the terminal. For example, if theforeign material on the surface of the fingerprint sensor is water andthe water can be removed within 10 seconds by increasing the temperatureof the fingerprint sensor, then a value of the preset time can be 10seconds.

When the temperature of the fingerprint sensor has been increased forthe preset time, determine whether the foreign material is on thesurface of the fingerprint sensor. If the foreign material is on thesurface of the fingerprint sensor, it means that increasing thetemperature of the fingerprint sensor is not sufficient to remove theforeign material. Then the message indicating that the foreign materialis present on the surface of the fingerprint sensor is sent, to promptthe user to remove the foreign material, thus ensuring that the foreignmaterial on the surface of the fingerprint sensor can be removedcompletely.

If the foreign material on the surface of the fingerprint sensor iswater, the water will be removed with the increasing of the temperatureof the fingerprint sensor within the preset time. If the foreignmaterial present on the surface of the fingerprint sensor is stilldetected after the preset time has elapsed, it indicates that theforeign material on the surface of the fingerprint sensor may be aforeign material that cannot be removed by increasing the temperature ofthe fingerprint sensor. The message indicating that the foreign materialis present on the surface of the fingerprint sensor is then sent, so asto prompt the user to remove foreign material.

According to the method for determining existence of the foreignmaterial on the surface of the fingerprint sensor of the secondimplementation, whether the foreign material is present on the surfaceof the fingerprint sensor is determined based on capacitance valuechanges of the fingerprint sensor, therefore, the operation ofdetermining existence of the foreign material present on the surface ofthe fingerprint sensor of the terminal can be simplified and theaccuracy of determining existence of the foreign material present on thesurface of the fingerprint sensor of the terminal can be improved.Moreover, the foreign material is removed in the preset manner, thusimproving the fingerprint recognition rate of the fingerprint sensor.

Third Implementation

FIG. 3 is a schematic structural diagram illustrating an apparatus fordetermining existence of a foreign material on a surface of afingerprint sensor according to a third implementation of the presentdisclosure. As illustrated in FIG. 3, the apparatus of the thirdimplementation includes a capacitance-value obtaining unit 31, adifference calculating unit 32, and a foreign-material determining unit33. The capacitance-value obtaining unit 31 can be coupled with afingerprint sensor.

The capacitance-value obtaining unit 31 can be a detector, a sensor, ora detecting circuit, and is configured to obtain a current capacitancevalue of a fingerprint sensor of a terminal at different stages. Forexample, the capacitance-value obtaining unit 31 can obtain the currentcapacitance value after a user touches the surface of the fingerprintsensor, or, it can obtain the current capacitance value of thefingerprint sensor when a preset time has elapsed after increasing thetemperature of the fingerprint sensor. The capacitance-value obtainingunit 31 can obtain the current capacitance value at preset intervals orbased on a certain event, such as a press or touch operation on thesurface of the fingerprint sensor by the user.

The difference calculating unit 32 can be a calculator, a counter, or acalculating circuit, and is configured to calculate a difference betweenthe current capacitance value and a preset capacitance reference value.

The foreign-material determining unit 33 can be a processor and isconfigured to determine that the foreign material is present on thesurface of the fingerprint sensor, if the first difference is within apreset foreign-material threshold range.

As illustrated in FIG.3, the apparatus may further include aforeign-material removal control unit 34, which can be implemented as amicro-controller or a logic control circuit. The foreign-materialremoval control unit 34 is generally configured to remove the foreignmaterial in a preset manner.

As one implementation, the foreign-material removal control unit 34 mayfurther include an alerting unit 35, which can be implemented as atransmitter, a sensor, an alarm system, and the like, and is configuredto send a message indicating that the foreign material is on the surfaceof the fingerprint sensor, to prompt a user to remove the foreignmaterial.

As another implementation, the foreign-material removal control unit 34may further include a temperature controller 36, which is configured toincrease a temperature of the fingerprint sensor, to remove the foreignmaterial. For example, in order to increase the temperature of thefingerprint sensor the temperature controller can be configured toincrease the power of the fingerprint sensor or can be configured tocontrol a heating device corresponding to the fingerprint sensor to heatthe fingerprint sensor.

The method for determining the existence of the foreign material on thesurface will be described in combination with the apparatus describedabove.

At the beginning, a current capacitance value of the fingerprint sensorof a terminal is obtained by the capacitance-value obtaining unit 31.Then a first difference between the current capacitance value and apreset capacitance reference value is calculated by the differencecalculating unit 32. If the first difference is within a presetforeign-material threshold range, the foreign-material determining unit33 determines that the foreign material is present on the surface of thefingerprint sensor. Otherwise, the foreign-material determining unit 33determines the surface of the fingerprint sensor with no foreignmaterial. Thereafter, the foreign material is removed in a preset mannervia the foreign-material removal control unit 34.

The foreign material can be removed by increasing temperature by thetemperature controller 36; in another implementation, the foreignmaterial can be removed by informing the user to remove it, such asissue an alert by the alerting unit 35.

In case that the temperature of the fingerprint sensor is increased, thecurrent capacitance value (that is, the second current capacitancevalue) of the fingerprint sensor of the terminal is obtained after apreset time has elapsed after increasing the temperature by thecapacitance-value obtaining unit 31. Then a second difference betweenthe second current capacitance value and the preset capacitancereference value is calculated by the difference calculating unit 32.Then determine that the foreign material is present on the surface ofthe fingerprint sensor by foreign-material determining unit 33 when thesecond difference is within the preset foreign-material threshold range.Thereafter, the alerting unit 35 will send the message indicating thatthe foreign material is present on the surface of the fingerprintsensor, so as to prompt the user to remove the foreign material.

The foregoing functional units can be implemented by a processorinvoking program codes stored in a memory, which will be described belowin detail.

Fourth Implementation

FIG. 4 is a schematic structural diagram illustrating a terminalaccording to a fourth implementation of the present disclosure.

As illustrated in FIG.4, a terminal 400 includes a processor 402, amemory 404, a fingerprint sensor 406, a communication interface 408, anda bus 410. The processor 402, the memory 404, the fingerprint sensor406, and the communication interface 408 can be coupled and communicatedvia the bus 410.

The processor 402 may be one of a central processing unit (CPU), amicro-processor, an application-specific integrated circuit (ASIC), orone or more integrated circuits for controlling the programs for theimplementation of above-mentioned technical solutions, and controlswireless communication with an external cellular network via thecommunication interface 408. The communication interface 408 includes,but is not limited to, an antenna, an amplifier, a transceiver, acoupler, a low noise amplifier (LNA), a duplexer and so on, and isconfigured to communicate with other devices or communication networkssuch as Ethernet, radio access network (RAN), wireless local areanetwork (WLAN) and the like. The fingerprint sensor 406 is configured toacquire fingerprint data of a finger of a user. The memory 404 includesat least one of a random access memory (RAM), a non-volatile memory, andan external memory, the memory 404 is configured to store executableprogram codes that executes the above-mentioned technical schemes and iscontrolled by the processor 402. The executable program codes can guidethe processor 402 to execute the method for determining the existence ofthe foreign material on the surface of the fingerprint sensor disclosedin the method implementation with reference to FIG.3 of the presentdisclosure. The memory 404 can exist independently and connect to theprocessor 402 via the bus 410. The memory 404 can also be integratedwith the processor 402.

The memory 404 is configured to store program codes which when executedby the processor 402 become operational with the processor 402 to:obtain a current capacitance value of the fingerprint sensor of aterminal; calculate a first difference between the current capacitancevalue and a preset capacitance reference value; determine that theforeign material is present on the surface of the fingerprint sensor,when the first difference is within a preset foreign-material thresholdrange.

The processor 402 is further configured to: remove the foreign materialin a preset manner.

The processor configured to remove the foreign material in a presetmanner is configured to: send a message indicating that the foreignmaterial is present on the surface of the fingerprint sensor, to prompta user to remove the foreign material; and/or increase a temperature ofthe fingerprint sensor, to remove the foreign material.

In one implementation, the processor 402 configured to increase atemperature of the fingerprint sensor is configured to execute one of:increasing a power of the fingerprint sensor, to increase thetemperature of the fingerprint sensor; controlling a heating devicecorresponding to the fingerprint sensor to heat the fingerprint sensor,to increase the temperature of the fingerprint sensor.

In another implementation, the processor 402 configured to increase atemperature of the fingerprint sensor is further configured to: obtainthe current capacitance value of the fingerprint sensor of the terminalwhen a preset time has elapsed after increasing the temperature of thefingerprint sensor; calculate a second difference between the currentcapacitance value of the fingerprint sensor of the terminal and thepreset capacitance reference value; determine that the foreign materialis present on the surface of the fingerprint sensor when the seconddifference is within the preset foreign-material threshold range; send amessage indicating that the foreign material is present on the surfaceof the fingerprint sensor, to prompt a user to remove the foreignmaterial.

In still another implementation, the processor 402 is further configuredto: set the preset foreign-material threshold range according toexperimental data of capacitance change tests which are performed on thefingerprint sensor when different conductive foreign materials arepresent on the surface of the fingerprint sensor.

It should be noted that, those of ordinary skill in the art mayunderstand that all or part of the steps in the methods of the foregoingimplementations may be implemented by a program instructing relevanthardware. The program may be stored in a computer-readable storagemedium such as the memory of the terminal and executed by at least oneprocessor of the terminal. When executed, the program may includeprocedures of the implementations such as the method for determining theexistence of the foreign material on the surface of the fingerprintsensor. The storage medium includes but is not limited to a Read OnlyMemory (ROM), a Random Access Memory (RAM), a magnetic disk, an opticaldisk, or the like.

Note that the above are exemplary implementations of the presentdisclosure and the applied technical principles. Those skilled in theart should understand that the present disclosure is not limited to thespecific implementations described herein, and various changes,modifications, and substitutions can be made by those skilled in the artwithout departing from the scope of the present disclosure. Although hasbeen described in detail by way of implementations, the presentdisclosure is not limited to the above implementations and otherequivalent implementations may be obtained without departing from thepresent disclosure. The scope of the present disclosure should bedetermined by the appended claims.

What is claimed is:
 1. A method for determining existence of a foreignmaterial on a surface of a fingerprint sensor, comprising: obtaining acurrent capacitance value of the fingerprint sensor of a terminal;calculating a first difference between the current capacitance value anda preset capacitance reference value; and determining that the foreignmaterial is present on the surface of the fingerprint sensor, when thefirst difference is within a preset foreign-material threshold range. 2.The method of claim 1, further comprising: subsequent to determiningthat the foreign material is present on the surface of the fingerprintsensor, removing the foreign material in a preset manner.
 3. The methodof claim 2, wherein removing the foreign material in the preset mannercomprises: sending a message indicating that the foreign material ispresent on the surface of the fingerprint sensor to prompt a user toremove the foreign material.
 4. The method of claim 2, wherein removingthe foreign material in the preset manner comprises: increasing atemperature of the fingerprint sensor to remove the foreign material. 5.The method of claim 4, further comprising: after increasing atemperature of the fingerprint sensor: obtaining the current capacitancevalue of the fingerprint sensor of the terminal that has been subjectedto the removing of the foreign material, when a preset time has elapsed;calculating a second difference between the current capacitance value ofthe fingerprint sensor of the terminal that has been subjected to theremoving of the foreign material and the preset capacitance referencevalue; determining that the foreign material is present on the surfaceof the fingerprint sensor when the second difference is within thepreset foreign-material threshold range; and sending a messageindicating that the foreign material is present on the surface of thefingerprint sensor to prompt a user to remove the foreign material. 6.The method of claim 4, wherein increasing the temperature of thefingerprint sensor comprises one of: increasing a power of thefingerprint sensor to increase the temperature of the fingerprintsensor; and controlling a heating device corresponding to thefingerprint sensor to heat the fingerprint sensor for increasing thetemperature of the fingerprint sensor.
 7. The method of claim 1, furthercomprising: before determining that the foreign material is present onthe surface of the fingerprint sensor when the first difference iswithin the preset foreign-material threshold range, setting the presetforeign-material threshold range according to experimental data ofcapacitance change tests performed on the fingerprint sensor whendifferent conductive foreign materials are present on the surface of thefingerprint sensor.
 8. An apparatus for determining existence of aforeign material on a surface of a fingerprint sensor, comprising: aprocessor; and a memory, coupled with the processor and configured tostore program codes which when executed by the processor becomeoperational with the processor configured to: obtain a currentcapacitance value of the fingerprint sensor of a terminal; calculate afirst difference between the current capacitance value and a presetcapacitance reference value; and determine that the foreign material ispresent on the surface of the fingerprint sensor, when the firstdifference is within a preset foreign-material threshold range.
 9. Theapparatus of claim 8, wherein the processor is further configured to:remove the foreign material in a preset manner.
 10. The apparatus ofclaim 9, wherein the processor configured to remove the foreign materialin the preset manner is further configured to: send a message indicatingthat the foreign material is present on the surface of the fingerprintsensor to prompt a user to remove the foreign material.
 11. Theapparatus of claim 9, wherein the processor configured to remove theforeign material in the preset manner is further configured to: increasea temperature of the fingerprint sensor to remove the foreign material.12. The apparatus of claim 11, wherein the processor configured toincrease the temperature of the fingerprint sensor is further configuredto: obtain the current capacitance value of the fingerprint sensor ofthe terminal when a preset time has elapsed after increasing thetemperature of the fingerprint sensor; calculate a second differencebetween the current capacitance value of the fingerprint sensor of theterminal and the preset capacitance reference value; determine that theforeign material is present on the surface of the fingerprint sensorwhen the second difference is within the preset foreign-materialthreshold range; and send a message indicating that the foreign materialis present on the surface of the fingerprint sensor, to prompt a user toremove the foreign material.
 13. The apparatus of claim 11, wherein theprocessor configured to increase a temperature of the fingerprint sensoris further configured to execute one of: increasing a power of thefingerprint sensor, to increase the temperature of the fingerprintsensor; and controlling a heating device corresponding to thefingerprint sensor to heat the fingerprint sensor, wherein thetemperature of the fingerprint sensor is increased.
 14. The apparatus ofclaim 8, wherein the processor is further configured to: set the presetforeign-material threshold range according to experimental data ofcapacitance change tests performed on the fingerprint sensor whendifferent conductive foreign materials are present on the surface of thefingerprint sensor.
 15. A terminal, comprising: a fingerprint sensor; acapacitance-value obtaining unit, coupled with the fingerprint sensor,and configured to obtain a current capacitance value of the fingerprintsensor at different stages; a difference calculating unit, configured tocalculate a difference between the current capacitance value and apreset capacitance reference value; and a foreign-material determiningunit, configured to determine that a foreign material is on a surface ofthe fingerprint sensor, when the difference is within a presetforeign-material threshold range.
 16. The terminal of claim 15, furthercomprising: a foreign-material removal control unit, configured toremove the foreign material in a preset manner.
 17. The terminal ofclaim 16, wherein the foreign-material removal control unit comprises:an alerting unit, configured to send a message indicating that theforeign material is present on the surface of the fingerprint sensor toprompt a user to remove the foreign material.
 18. The terminal of claim16, wherein the foreign-material removal control unit comprises: atemperature controller, configured to increase a temperature of thefingerprint sensor to remove the foreign material.
 19. The terminal ofclaim 18, wherein the capacitance-value obtaining unit is configured toobtain the current capacitance value of the fingerprint sensor of theterminal when a preset time has elapsed after increasing the temperatureof the fingerprint sensor.
 20. The terminal of claim 18, wherein thetemperature controller is configured to execute one of: increase a powerof the fingerprint sensor to increase the temperature of the fingerprintsensor; and control a heating device corresponding to the fingerprintsensor to heat the fingerprint sensor, wherein the temperature of thefingerprint sensor is increased.